Recently the concept of dividing higher plants into two distinct groups has reveived much attention. One group of the plants, C4-Cycle plants, is characterized by fixing CO2 photosynthetically two to three times higher than the other group of the plants, Calvin Cycle plants. The C4-Cycle plants such as corn, sugarcane, and some tropical grasses contain two types of chloroplasts and fix CO2 via the combination of C4- Cycle and Calvin Cycle; the chloroplast of mesophyll cells is responsible for the operation of C4-Cycle and the chloroplast of bundle sheath cells for the operation of Calvin Cycle. The chloroplasts in two cell types in C4-Cycle plants may function cooperatively in photosynthetic CO2 fixation based on enzymes distribution and morphological studies of two cell types. However, it is still not known yet whether two chloroplast types work independently or they depend on each other in the light-driven synthesis of ATP and NADPH and/or photosynthetic CO2 fixation. The goal of the proposed research is to isolate a large quantity of bundle sheath cells and mesophyll cells from leaf of C4-Cycle plants and to study their comparative biochemistry of mechanism of oxygen evolution and ATP formation. Since both leaves of C4-Cycle plants and Calvin Cycle plants are able to metabolize herbicides, another major goal of their proposal will also be emphasized on the mode of action and the metabolism of herbicides in the isolated plant leaf cells or chloroplasts of two groups of higher plants.